Cellular plasticity endows epithelial cells the ability to adopt distinct downstream lineage fates. Epithelial cells can undergo epithelial-to-mesenchymal transition (EMT) to lose their epithelial properties and gain mesenchymal features to become migratory cell types during normal development and in various pathological conditions such as wound healing, organ fibrosis, and cancer metastasis. The goal of this project is to provide a molecular understanding of how, during active tissue morphogenesis, embryonic epidermal progenitor cells utilize positive and negative regulators of EMT to control proliferation, migratio, and terminal differentiation, all within the confinement of a committed epithelial lineage. The firt specific aim is to characterize the molecular function of two sister regulatory factors, Ovol1 and Ovol2. So far our studies have shown that these factors act as gatekeepers of epithelial identity and epidermal differentiation at least in part by suppressing EMT-like processes. We will employ a combination of genomic, molecular, and computational approaches to identify downstream targets of Ovol1 and Ovol2, and to elucidate critical regulatory strategies that coordinately control the intertwined cellular processes including epithelial plasticity, proliferation, and differentiation. The second specific aim is to determine the physiological significance of EMT-like events in epidermal development by studying the genetic and molecular functions of two related EMT-promoting factors, Zeb1 and Zeb2. We will generate mice lacking both Zeb1 and Zeb2 using existing mutants, and analyze the impact on epidermal morphogenesis. The last specific aim is to determine whether and how EMT-promoting and EMT-inhibiting pathways antagonize each other to ensure a delicate balance between epithelial plasticity and differentiation. Specifically, we will use molecular and mouse genetics to test the hypothesis that Zeb1 and Ovol2 mutually suppress each other's expression and function. The proposed studies hold great potential to uncover new molecular and genetic mechanisms that control epidermal development and differentiation. They will also establish the developing epidermis as a new paradigm for studying the transcriptional regulation of EMT-like processes in committed epithelial tissues. Finally, our proposed work will have profound implications for pathological human skin conditions, as defective epidermal development can lead to the formation of a malfunctioning skin permeability barrier, which is a major contributor to skin diseases such as atopic dermatitis.